The present invention relates to a fuel/air mixer for a combustor and more particularly to a focused application of air directly on the fuel spray as it is flowing out of a fuel injector to increase the transport of fuel spray during engine snap deceleration conditions.
One goal in the design of combustors, such as those used in gas turbine engines of high performance aircraft, is to minimize the amount of smoke produced by the combustion process in the gas turbine engine. For military aircraft in particular, smoke production creates a “signature” which may increase aircraft visibility.
Another objective in the design of combustors for high performance aircraft is to maximize the “static stability” of a combustor. The term “static stability” refers to the ability to initiate the combustion process at high airflows and low fuel flow during a rapid deceleration of the engine.
Leaning out the fuel/air mixture in the combustor minimizes smoke production, while static stability is increased by enriching the fuel/air mixture. Applicant has addressed the competing goals with a fuel injector design with an outer recirculation zone flame stabilization arrangement. Although effective, flame stability in such a fuel injector may still be relatively sensitive during snap deceleration conditions. Snap deceleration is of particular interest to the performance of military aircraft.
Spray transport is important to the operation of a fuel injector design intended for outer recirculation zone flame stabilization. Fuel is injected from a pressure atomizing fuel nozzle and reaches a prefilmer wall by one of two mechanisms. The first is a centrifuge mechanism. Large drops in a rotating environment are slung outboard to the prefilmer wall. A second mechanism is from velocity of the fuel itself. This fuel velocity typically results from the pressure available in the fuel system.
Conventional fuel injector systems may not provide sufficient spray transport across an inner passage airflow to reach the prefilmer wall under snap deceleration conditions as droplet sizes may be too small for effective centrifuge action to take place in the space available. Furthermore, there may be insufficient pressure drop across the fuel injector tip to provide sufficient velocity to traverse the inner passage at the fuel flow common to snap deceleration conditions. Such conventional fuel nozzle systems may thus suffer a loss in flame stability during snap deceleration conditions.
Accordingly, it is desirable to provide a fuel injector system that minimizes the amount of smoke production while maximizing stability even under snap deceleration conditions.